1. Field of the Invention
The present invention relates to an evaporated fuel treatment device for an internal combustion engine.
2. Description of the Related Art
As a device for reducing an evaporation fuel which is permitted to be naturally evaporated from a fuel system, particularly a fuel tank, to the atmosphere for an internal combustion engine, there is an fuel vapor discharge suppressing device. In the fuel vapor discharge suppressing device of this type, an activated carbon canister is generally employed.
The activated carbon canister includes a vessel in which activated carbon is accumulated, and is designed in such a manner that, for example, when an internal combustion engine is stopped, the fuel vapor generated from the fuel system is introduced into the vessel so as to be adsorbed by the activated carbon. The fuel vapor discharge suppressing device is communicated with a inlet passage of the internal combustion engine so that the fuel vapor adsorbed by the activated carbon is attracted to the inlet passage from the activated carbon by a negative pressure in the inlet passage when the internal combustion engine is operated and then purged. The fuel vapor thus purged is burned together with air-fuel mixture. The activated carbon thus purged is recovered in adsorption capacity, and repeatedly functions.
In the recent years, an internal combustion engine having a variable valve timing mechanism has been spread, and there is proposed that the above-mentioned fuel vapor discharge suppressing device is applied to this internal combustion engine.
The variable valve timing mechanism is designed, as well known, so as to adjust a valve overlapped amount by varying an open/close timing of at least an intake valve among the inlet and exhaust valves according to the r.p.m. of the engine, as a result of which since the intake air flow into a combustion chamber is adjusted to enable the pumping loss to be reduced, a pressure in the inlet passage approaches the atmospheric pressure from the negative pressure. This makes it difficult to function the fuel vapor discharge suppressing device that employs the negative pressure in the inlet passage, and there is a worriment that the fuel vapor could not be purged from the canister. Therefore, in that case, it is estimated that the fuel vapor is overflowed from the canister, to thereby deteriorate the evaporative emission.
In order to cope with the above defect, there has been disclosed, for example, in Japanese Patent Unexamined Publication No. Hei 5-156973, an evaporated fuel treatment device for an internal combustion engine which is designed in such a manner that the fuel vapor can be purged even if the variable timing mechanism is operated in the case where the fuel vapor discharge suppressing device is applied to the internal combustion engine having the above variable value timing mechanism.
The fuel vapor treating device for the internal combustion engine of this type is designed such that the close timing of the intake valve is advanced, that is, the close timing of the intake valve is hastened to promote the negative pressure state in the inlet passage, thereby surely performing the purge from the canister to the inlet passage.
However, this device is structured such that the close timing of the intake valve is not spark-advanced until a predetermined condition for execution of the purge (purge execution condition) is satisfied under the condition where the canister evaporation adsorbs a predetermined amount or more of the fuel vapor. For that reason, in the case where the internal combustion engine is put in the condition where the fuel vapor is remarkably liable to occur, it is largely estimated that the amount of the generated fuel vapor is larger than the amount of purge. Assuming such a case, the above-described predetermined amount of the canister is usually set to be smaller than the maximum capacity of the canister. However, the canister is soon filled with the adsorbed fuel vapor, as a result of which there is a risk that the fuel vapor is overflowed from the canister.